Adjuvanted swine flu vaccine bests unboosted shot

LONDON (Reuters) - The first head-to-head study comparing swine flu vaccines in Britain found that children given a shot containing a booster, or adjuvant, had a stronger immune response than those receiving one without it.

GlaxoSmithKline's vaccine Pandemrix, containing the adjuvant AS03, was associated with more side effects than Baxter's Celvapan but experts said the somewhat higher rate of fevers and injection site irritations was not a major concern.

The use of adjuvants, which are designed to boost the body's response to a vaccine, has divided health authorities in Europe and the United States.

They were widely used in Europe last year to deal with the H1N1 swine flu pandemic. In the United States, however, officials stuck with the standard unadjuvanted formulation used in seasonal flu vaccines.

"I think this data is reassuring for countries such as the U.S. which haven't approved the use of adjuvants for influenza vaccines," researcher Dr Matthew Snape of the Oxford Vaccine Group at Oxford University said in a telephone interview.

"It may be that even for seasonal flu vaccines we should be looking at adjuvants such as AS03."

Pandemrix, which is produced using chicken eggs, was selected as the standard H1N1 vaccine in Britain, with Baxter's cell culture shot reserved for people with egg allergies.

Snape said both vaccines provided good protection and were well tolerated - but the strong response to Pandemrix in children under 3 years was particularly encouraging.

"This age group is most at risk from influenza and it is the age group that has generally not responded so well to vaccines in the past," he said.

Results of the study involving 900 children aged 6 months to 12 years, published in the British Medical Journal on Friday, showed a 98.2 percent immune response in children under three with Pandemrix against 80.1 percent for Celvapan.

In children over three, the difference was less marked, with so-called "seroconversion" rates of 99.1 percent after two doses of Pandemrix against 95.9 percent for Celvapan.

A higher immune response to vaccination generally means it lasts longer and it may provide protection if the flu virus changes. H1N1 is expected to be the dominant flu strain next winter but its genetic make-up is likely to drift slightly.